For example, a lithium ion secondary battery is known as a non-aqueous electrolyte secondary battery. The lithium ion secondary battery has high energy density, high operating voltage, small self-discharge, and superior features as compared with a conventional secondary battery such as a nickel-metal hydride battery or a lead storage battery. The lithium ion secondary battery is widely utilized for a small sized electronic equipment such as a laptop computer or a cellular phone and, furthermore, recently as a storage power supply of on-board and stationary type.
In manufacturing processes of the lithium ion secondary battery, after a sealing step of storing and sealing the electrode laminate in which separators are disposed between a plurality of electrodes and the electrolyte within the exterior body constituted by the laminate film, a charge step of charging up to a full charge is carried out.
In the sealing step or charge step, gas is generated in association with a reaction of the electrolyte. In order to prevent a reduction in the battery characteristics due to gas resided within the exterior body, a gas removal step of removing gas within the exterior body is carried out after the charge step. In such a gas removal step as described above, an operation of unsealing the exterior body is carried out.
A Patent Document 1 discloses the manufacturing method of the battery having a sealing step of sealing the electrode laminate and a particular filing material into the exterior body, a first charge step of charging up to less than a full charge voltage, and a second charge step of charging to the full charge. According to this manufacturing method, the gas removal step is carried out using a particular filling material after the first charge step so that unsealing the exterior body in order to remove gas after the second charge step is not needed.
However, in the manufacturing method described in the above-described Patent Document 1, although the gas removal step can be eliminated which is carried out after the second charge step, gas generated after the second charge step reduces the battery characteristics.
Hence, it is preferable to suppress an influence of gas on the battery characteristics, in the manufacturing method of the battery. In addition, in a case where the reduction of the battery characteristic due to a contact of the electrode or electrolyte on moisture in the air or oxygen and a safety of the manufacturing step are taken into consideration, it is desirable to reduce number of times of the gas removal steps which unseal the exterior body.
It is, therefore, an object of the present invention to provide a manufacturing method of a non-aqueous electrolyte secondary battery which can solve the above-described task.